I had a similar experience with a chicken. He injured his wing at the Fair. The on call vet took a look and it was just a bruise, no tendon damage or anything. He held his wing in a droopy mannor and wouldn't pick it up and even when he did it just flopped down again.
You need to examine his wing closely. Start by holding him on his back so that you can see the entire underside of his wing. Have someone help you if need be. Look for any dark purple or blue discolorations or any visible swelling. If you don't see any run your hand down the entire length of the wing feeling every bone and tendon for lumps. If you see a bruise or swelling feel the area around it. Often the injury, if there is one, will be toward the center of the swell or bruise. If there is a break you will feel a slight bump or knot that seems out of place, you may even see the break or feel the bone press against the skin. If there is no discoloration and you do not feel or see any signs of a break, then there most likely isn't one.
If he looks and feels fine, but is still holding his wing in a bad position and dragging it you will need to tie it up for a couple of days so that he can rest up. You can do this several ways.
The easiest is to cut the end off of a nylon stalking to make a tube. Cut a whole in one side of the stalking for the other wing to go through, so he can still use it. The other wing will remain inside the staking and be supported. Be sure the wing is in a natural position to ensure no further damage is done to it.
You can also wrap vet wrap around the injured wing to huld it up. Go underneath the good wing and wrap the injured one up tightly. Be sure he can still breath, but keep his wing immobilized. You can also use a bra, a pair of old elastic undies, an old shirt, etc. to tie up the wing.
Be sure you keep him separated from the flock, but where he can't see or hear them and panic. Give him lots of food, but only a small dish of water. No bathing water. Be sure the cage is fairly small to keep him from moving around.